There are a few different ways you can equip your heavy vehicle with a dash cam. The "classic" approach would be to install a Front-only Dash Cam (aka single-channel) for recording the road in front.
If you're a fleet owner who wants to record the employees operating the vehicle, please consider one of the Front+Interior Dash Cams allowing you to record inside the cabin as well as the road.
For the professional front and rear solution for heavy vehicles, the BlackVue TRUCK series is the perfect choice. With a waterproof externally-mounted rear camera with IR lights, this solution provides the most context to your driving.